Old Glaze Formulas

I wonder if anyone can shed some light on this. I found an old glaze book with some great recipes I remember in it. There were some that do not fit the glaze formula adding up to 100% and the additions normally take it over or are in addition to 100%. The two recipes below are examples of what I mean. They are more like a cake recipe made up of various ingredients in a random fashion, one formula adding up to 112% without additions and the other only 94%. The percentages were not with the recipes, I calculated them because the formula did not look correct.

Is this way of mixing glazes a correct way or is there a calculation you are supposed to use to convert the glazes so that they fit the 100% rule?

To convert a glaze recipe in any amount format to a glaze raw materials percentage relationship, add up the total of all the ingredients in the original recipe. Then divide each single ingredient item's original number by that overall total number. It will now be set up in a percentage format.

The usual "convention" in the filed is that the "main ingredients" add up to 100%, and then things like opacifiers, colorants, a small addition of benonite , and so on are above and beyond the total of the "base glaze". But this in no way is mandatory nor does it affect anything.

For those of us who also use molecular glaze calculation as a part of looking at glazes, it often helps to include the function of things like coloring oxides that act as fluxes or ampoterics into the main calculation....... but many people ignore this with everything except iron oxide.

best,

...............john

John BaymoreImmediate Past President; Potters CouncilProfessor of Ceramics; New Hampshire Insitute of Art

Thanks for your responses, I checked with a few other people around here and their responses were very similiar, so next step will be to just mix up some small batches and test them. These are actually from my old glaze book at Arizona State, so they have not been mixed by me in a very long time.